Handler from entry to continue
Android asynchronous message mechanism --Handler
Android's Handler mechanism is an inter-thread communication mechanism, to avoid time-consuming operation resulting in Activity timeout and closed issue in the main thread.
At first look this mechanism, see a lot of Looper, MessageQueue, Handler, etc., mentioned the source code level, I feel really unfathomable.
Process Handler mechanism
After reading a lot blog, I discovered that in fact when entry not look so complicated, just enough to know Handler, Handler can be translated as handler, who is handling the message meant. A thread is equivalent to his secretary, when A has things to do entrusted to B, B to inform the secretary called, the secretary told B done, he done, can be reported to the A, let A subsequent work to do .
The basic mechanism of usage Handler
Faith pragmatism, or start using the angle Handler Handler's speaking to sum up the usage of it.
Create an instance Handler
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
Log.d(TAG, "handleMessage: msg.what = " + msg.what + " msg.arg = " + msg.arg1);
switch (msg.what) {
case OVER:
text.setText("下载完成");
break;
case PROGRESS:
text.setText("已完成" + msg.arg1 + "%");
break;
default:
break;
}
}
};
HandleMessage need override method is to pass is determined by the message type msg.what, to enter a different service processing logic.
Incoming handler to the child thread
class DownloadThread extends Thread {
Handler handler;
public DownloadThread(Handler handler) {
this.handler = handler;
}
}
When it needed from the child thread return a message
Example simulation of a download operation, namely the sub-thread download incoming handler, the handler with the timing of a configuration Message, back to the main thread updates the display TextView.
@Override
public void run() {
while (progress < 100) {
Message response = Message.obtain(handler);
response.what = PROGRESS;
progress += 5;
if (progress == 100) {
response.what = OVER;
}
response.arg1 = progress;
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
response.sendToTarget();
}
}
- what
used to mark the message type, such as PROGESS, OVER which are used to represent the current state of the download. - arg1
is used to store the value of other messages, as described in Example arg1 for storing the download progress.
Epilogue
Okay, so a simple demo handler mechanism is complete. Android framework for us to complete setting up the mechanism observer, we need to do is to construct a good handler in the business processing logic in the main thread and the child thread of messages to feedback.
